$ { {-1} \times \left[\begin{array}{rr}{2} & {-1} \\ {-1} & {0}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-1}\times{2} & {-1}\times{-1} \\ {-1}\times{-1} & {-1}\times{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-2} & {1} \\ {1} & {0}\end{array}\right]}$